1. Field of the Invention
The present invention relates to an optical sheet and an optical sheet lamination (xe2x80x9claminationxe2x80x9d includes stacking or putting on in not contact with another) composed of a prism sheet, a lens sheet and/or an optical diffusing sheet suitable for use in a back light surface light source used in illuminating from the back a light-transmissive type display panel of a light-transmissive type liquid crystal display apparatus, an advertising board or the like, and a surface light source device and a light-transmissive type display apparatus using the same optical sheet or optical sheet lamination.
2. Prior Art
In a liquid crystal display apparatus in recent years, according to necessity of reducing of its power consumption and making it thin and light in shape and weight, a surface light source for illuminating the liquid crystal display apparatus from the back has been naturally required also to be made thin and light in shape and weight and has been reduced in power consumption in its light source by effectively utilizing light from the light source for reduction of power consumption.
In response to such requirement, such techniques for directing light from a surface light source in a particular direction (in the normal direction to a light outputting surface in many cases) have been proposed as disclosed in Japanese laid-open publication Tokkaisho No. 60-70601, Tokkaihei No. 2-84618, Jikkaihei No. 3-69184, Tokkaihei No. 7-191319 and the like.
As a surface light source device used in a light-transmissive type liquid crystal display apparatus and the like there are light source devices of an edge-light type and of a direct back light type.
A surface light source device of an edge-light type, as disclosed in a Japanese laid-open publication Tokkaihei No. 3-5725, has a light-source light inputted into it usually through one side end surface of a plate-shaped light guide means of a transparent acryl resin or the like, leads the light to an light outputting surface which is the other surface of the light guide means, and therefrom outputs the light to the back surface of a liquid crystal panel or the like.
In such a case, in order to improve the efficiency of utilizing light, an optical reflector plate or an optical reflector film is often provided on the opposite surface of said light guide means to the light outputting surface and in order to make the output light uniform, a light diffusing sheet having a light diffusing function is often provided at the light outputting surface side of the light guide means, as disclosed in a Japanese laid-open publication Jikkaihei No. 5-73602 and the like, for example.
A surface light source device of a direct back light type, as disclosed in a Japanese laid-open publication Jikkaihei No. 2-33001 for example, generally reflects a light-source light onto the back surface of a liquid crystal panel or the like by means of a reflector plate and diffuses its output light by means of a light diffusing sheet disposed at the light outputting surface side so that the shape of the light source cannot be identified by human eyes.
Some of such surface light source devices of an edge-light type or a direct back light type as described above are provided with a prism sheet (prism film) or a lens sheet (lens film) which has an array of plural unit prisms or plural unit lenses arranged on the obverse surface of the light-transmissive base material of it in order to output light from a surface light source collectively in a particular direction, as described above.
Various applications of such optical sheets have been proposed in combination of plural optical sheets and in direction of setting the side at which unit prisms or unit lenses are formed (prism side or lens side) with regard to the light source side.
In such an optical sheet as described above, the opposite surface (reverse surface) to the prism surface or lens surface is often formed into a flat and smooth surface.
In an optical sheet as described above, a pattern where bright and dark parts are alternately repeated by light from a surface light source is observed in case of combination of a light guide means, a diffusing sheet, another optical sheet and the like, and a problem that an image composed of pixels is disarranged has been caused by this in case that such an optical sheet is used in a liquid crystal display apparatus, for example.
On the other hand, as disclosed in a Japanese laid-open publication Tokkaihei No. 7-151909 for example, a method for solving this problem has been proposed on the assumption that said pattern of repeating bright and dark parts is caused by interference fringes generated by an outside light source between the prism surface of one prism sheet and the flat and smooth surface of the other prism sheet in case of using two prism sheets, for example.
When we have checked this assumption, however, a pattern of repeating bright and dark parts has been observed in a surface light source device even in a darkroom where no light enters from any outside light source.
That is to say, we have confirmed that interference fringes are generated by a surface light source rather than an outside light source and further generated between the flat and smooth surface of a prism sheet and the flat and smooth face of a light guide plate or the flat and smooth surface of a diffusing plate or other prism sheets.
On the other hand, a method of forming minute rugged parts satisfying a particular condition on the flat and smooth surface of a prism sheet is also conceivable as disclosed in said Tokkaihei No. 7-151909, but in this case, there is a problem that the primary function of a prism sheet for improving the brightness by collecting light from a surface light source in a particular direction, for example, in the normal direction to the light outputting surface is deteriorated.
As for the light outputting side, many existing prism sheets as described above are made so as to cover defects (flaws, stains and the like) of a prism sheet by laminating a light diffusing sheet on the prism surface side which is a light outputting surface and are somewhat weakened in directivity of their light outputting characteristics.
Such a prism sheet having a light diffusing sheet laminated on it has a problem that a prism (or lens) part touching the light diffusing sheet is damaged by a rugged part on the surface of the light diffusing sheet and this flaw deteriorates a uniform and flat light-emitting state as a whole.
On the other hand, although a method of forming the prism sheet side of a light diffusing sheet into a flat and smooth surface in the same way as the light inputting surface of said prism sheet is also conceivable, such a method as this has not come to be in practical use since there is a problem that interference fringes or moire patterns are generated between the flat and smooth surface of said light diffusing sheet and the flat and smooth surface of a light guide plate or the flat and smooth surface of a prism sheet.
The present invention has been performed in consideration of the above-mentioned existing problems, and an object of the invention is to provide an optical sheet and an optical sheet lamination (in the present invention, xe2x80x9claminationxe2x80x9d includes stacking or putting on in not contact with another) which are made so as to suppress deterioration in brightness of the light outputting side and generation of interference fringes and so as not to damage other prism sheets being in contact with them, and a surface light source device and a light-transmissive type display apparatus using the same optical sheet and optical sheet lamination.
The present invention attains the above-mentioned object by means of an optical sheet which has one surface of its light-transmissive base material on which at least one of a group of plural unit prisms and a group of plural unit lenses is arranged and the other surface of it coated with a coating layer formed out of light-transmissive materials, wherein said coating layer is composed of a light-transmissive resin and light-transmissive fine particles dispersed in this light-transmissive resin, and at least part of said fine particles form a number of fine knoll-shaped projections of 1 to 10 xcexcm in height projecting from said surface by being projected from the opposite surface of said coating layer to the light-transmissive base material.
The coating layer in said optical sheet may be 2 to 20 xcexcm in thickness including said fine knoll-shaped projections.
The fine knoll-shaped projections in said optical sheet may be disposed at random along said surface of said coating layer.
At least part of the fine particles in said optical sheet may be composed of light-transmissive beads of 1 to 10 xcexcm in particle diameter.
The fine particles in said optical sheet may be composed of spherical beads of 1 xcexcm or less in half bandwidth of the distribution of particle diameters.
The ratio of the refractive index of a material forming the fine particles in said optical sheet to the refractive index of a light-transmissive resin of said coating layer may be 0.9 to 1.1.
The coating layer in said optical sheet may be formed by applying and drying an ink to the reverse surface of said light-transmissive base material, said ink being obtained by mixing with each other said light-transmissive resin and said light-transmissive beads less in specific gravity than this resin, and said fine knoll-shaped projections are formed by projecting said light-transmissive beads from said ink-coated film which has dried and contracted.
At least part of fine particles in said optical sheet may be formed out of light-transmissive beads, and said light-transmissive beads are distributed unevenly more at the opposite surface side of said coating layer to the light-transmissive base material and projected from said surface.
The coating layer in said optical sheet may be formed by applying an ink obtained by mixing with each other said light-transmissive resin and said light-transmissive beads less in specific gravity than this resin to the reverse surface of said light-transmissive base material so as to be pressed by gravity, and by hardening the ink after said light-transmissive beads come to be distributed unevenly more in the vicinity of the surface after the ink has been applied.
The present invention attains the above-mentioned object by means of an optical sheet which has one surface of its light-transmissive base material on which at least one of a group of plural unit prisms and a group of plural unit lenses is arranged and the other surface of it coated with a coating layer formed out of light-transmissive materials, wherein said coating layer is composed of a light-transmissive resin and light-transmissive beads which are dispersed in this light-transmissive resin, 1 to 10 xcexcm in particle diameter and 1 xcexcm or less in half bandwidth of the distribution of particle diameters, and at least part of said light-transmissive beads are projected from the opposite surface of said coating layer to the light-transmissive base material and thereby many fine knoll-shaped projections of 1 to 10 xcexcm in height projecting from said surface are formed and said coating layer is formed to be 2 to 20 xcexcm in thickness including said fine knoll-shaped projections, and the ratio of the refractive index of a material forming said light-transmissive beads to the refractive index of the light-transmissive resin in the coating layer is 0.9 to 1.1.
The light-transmissive beads in said optical sheet may be distributed unevenly more at the opposite surface side of said coating layer to the light-transmissive base material and projected from said surface.
And the present invention attains the above-mentioned object by means of an optical sheet having a light-transmissive base material having one surface having a light diffusing layer on it and the other surface covered with a coating layer formed out of a light-transmissive material, said coating layer comprising light-transmissive spherical beads of 1 xcexcm or less in half bandwidth of the distribution of particle diameters.
The light diffusing layer in said optical sheet may be formed so as to contain light-transmissive beads, and the average particle diameter of the light-transmissive spherical beads in this light diffusing layer may be made larger than the average particle diameter contained in said coating layer.
The spherical beads contained in the coating layer in said optical sheet may be 1 to 10 xcexcm in particle diameter.
The present invention attains the said object by means of an optical sheet lamination which is formed by laminating together plural optical sheets containing unit prisms or unit lenses, wherein each optical sheet has plural unit prisms or unit lenses arranged on one surface of a light-transmissive base material and the other surface being covered with a coating layer formed out of a light-transmissive material, said coating layer contains light-transmissive spherical beads of 1 xcexcm or less in half bandwidth of the distribution of particle diameters, and said coating layer in the laminated optical sheet is in contact with unit prisms or unit lenses of another optical sheet laminated adjacently to it.
Moreover, the present invention attains the said object by means of an optical sheet lamination which is formed by laminating together one or more optical sheets each of which has a light-transmissive base material having one surface having a light diffusing layer on it and the other surface covered with a coating layer formed out of light-transmissive materials, said coating layer containing light-transmissive spherical beads of 1 xcexcm or less in half bandwidth of the distribution of particle diameters, and one or more optical sheets each of which has plural unit prisms or plural unit lenses arranged on the surface of a light-transmissive base material, wherein said coating layer in an laminated optical sheet is in contact with unit prisms or unit lenses of another optical sheet laminated adjacently to it.
The vertical angle of the tops of said prisms or lenses of the optical sheets being in contact with the coating layer of another optical sheet may be as sharp as 100xc2x0 or less.
And the present invention attains the said object by means of a surface light source device composed of a light source for outputting light from its light outputting surface and an optical sheet provided adjacently to said light outputting surface, said optical sheet having one surface of a light-transmissive base material on which at least one of a group of plural unit prisms and a group of plural unit lenses is arranged and the other surface being covered with a coating layer formed out of light-transmissive materials, wherein said coating layer is composed of a light-transmissive resin and light-transmissive fine particles dispersed in this light-transmissive resin, and at least part of said fine particles are formed into many fine knoll-shaped projections of 1 to 10 xcexcm in height projecting from said surface by being projected from the opposite surface of said coating layer to the light-transmissive base material.
The coating layer in said optical sheet may be 2 to 20 xcexcm in thickness including said fine knoll-shaped projections.
At least part of the fine particles in said surface light source device may be light-transmissive beads of 1 to 10 xcexcm in particle diameter.
Said fine particles in the coating layer of said surface light source device may be spherical beads of 1 xcexcm or less in half bandwidth of the distribution of particle diameters.
The ratio of the refractive index of a material forming the fine particles in said surface light source device to the refractive index of a light-transmissive resin of said coating layer may be 0.9 to 1.1.
At least one lens sheet which has one surface of a light-transmissive base material in said surface light source on which at least one of a group of plural unit prisms and a group of plural unit lenses arranged, and the other surface being made flat and smooth without raggedness by being covered with a coating layer formed out of a light-transmissive material is put between said optical sheet and said light outputting surface.
A light source in said surface light source device may be composed of a light guide means which is a plate-shaped member one of whose surfaces is said light outputting surface and which outputs a light introduced through at least one side end surface from said light outputting surface, and a light generating source for inputting light into said light guide means through at least said one side end surface of said light guide means.
A light diffusing sheet may be disposed on the light outputting surface of the light source in said surface light source device and the light outputted through said light diffusing sheet from said light outputting surface may be inputted from said coating layer side.
At least part of said fine particles in said surface light source device may be formed out of light-transmissive beads, and said light-transmissive beads may be distributed unevenly more at the opposite surface side of said coating layer to the light-transmissive base material and may be formed into many fine knoll-shaped projections by being projected from said surface.
The present invention attains the said object by means of a surface light source device composed of a light source for outputting light from its light outputting surface and an optical sheet provided adjacently to said light outputting surface, said optical sheet having one surface of a light-transmissive base material on which at least one of a group of plural unit prisms and a group of plural unit lenses is arranged and the other surface being covered with a coating layer formed out of light-transmissive materials, wherein said coating layer comprises light-transmissive spherical beads of 1 xcexcm or less in half bandwidth of the distribution of particle diameters and the light outputted from said light outputting surface is inputted from said coating layer side.
Said light diffusing layer in said surface light source device may comprise light-transmissive spherical beads, and the average particle diameter of the light-transmissive spherical beads in said light diffusing layer may be larger than the average particle diameter of the spherical beads contained in said coating layer.
The spherical beads contained in the coating layer in said surface light source device may be 1 to 10 xcexcm in particle diameter.
The present invention attains the said object by means of a surface light source device composed of a light source for outputting light from its light outputting surface and an optical sheet provided adjacently to said light outputting surface, said optical sheet having one surface of a light-transmissive base material on which at least one of a group of plural unit prisms and a group of plural unit lenses is arranged and the other surface being covered with a coating layer formed out of light-transmissive materials, wherein said coating layer contains a light-transmissive resin and light-transmissive beads, dispersed in this light-transmissive resin, of 1 to 10 xcexcm in particle diameter and 1 xcexcm or less in half bandwidth of the distribution of particle diameters, and at least part of said light-transmissive beads are formed into many fine knoll-shaped projections of 1 to 10 xcexcm in height projecting from the opposite surface of said coating layer to the light-transmissive base material by being projected from said opposite surface, and said coating layer is 2 to 20 xcexcm in thickness including said fine knoll-shaped projections, and the ratio of the refractive index of a material forming said light-transmissive beads to the refractive index of the light-transmissive resin in the coating layer is 0.9 to 1.1.
The light-transmissive beads in said surface light source device may be distributed unevenly more at the opposite surface side of said coating layer to the light-transmissive base material and projected from said surface.
The vertical angle of the tops of said prisms or lenses of the optical sheets being in contact with the coating layer of another optical sheet may be as sharp as 100xc2x0 or less.
The present invention attains the said object by means of a light-transmissive type display apparatus composed of a flat light-transmissive display means and a surface light source device which is disposed at the back of said light-transmissive display means and irradiates said light-transmissive display means from the back with its output light, wherein said surface light source device is composed of a light source for outputting light from its light outputting surface and an optical sheet provided adjacently to said light outputting surface, said optical sheet having one surface of a light-transmissive base material on which at least one of a group of plural unit prisms and a group of plural unit lenses is arranged and the other surface being covered with a coating layer formed out of light-transmissive materials, and light-transmissive fine particles different from a material for the coating layer are disposed on the opposite surface of said coating layer to the light-transmissive base material and thereby many fine knoll-shaped projections of 1 to 10 xcexcm in height projecting from said surface are formed, and the light outputted from said light outputting surface is inputted from said coating layer side.
Said coating layer of the optical sheet in said light-transmissive type display apparatus may be 2 to 20 xcexcm in thickness including said fine knoll-shaped projections.
At least part of said fine particles of the optical sheet in said light-transmissive type display apparatus may be light-transmissive beads of 1 to 10 xcexcm in particle diameter.
Said fine particles of the coating layer of the optical sheet in said light-transmissive type display apparatus may be spherical beads of 1 xcexcm or less in half bandwidth of the distribution of particle diameters.
The ratio of the refractive index of a material forming said fine particles of the optical sheet in said light-transmissive type display apparatus to the refractive index of the light-transmissive resin of the coating layer may be is 0.9 to 1.1.
At least one lens sheet which has one surface of a light-transmissive base material in said light-transmissive display apparatus on which at least one of a group of plural unit prisms and a group of plural unit lenses is arranged and the other surface being made flat and smooth without raggedness by being covered with a coating layer of a light-transmissive material may be put between said optical sheet and said light outputting surface in said surface light source device.
Said light source of said surface light source device in said light-transmissive type display apparatus may be composed of a light guide means which is a plate-shaped member, formed out of a light-transmissive material, having one surface of it as said light outputting surface and outputs a light inputted from at least one side end surface through said light outputting surface, and a light generating source for inputting light from at least said one side end surface of said light guide means into it.
A light diffusing sheet may be disposed on the light outputting surface of said light source in said light-transmissive type display apparatus, and a light outputted through said light diffusing sheet from said light outputting surface may be inputted from said coating layer side.
At least part of said fine particles of the optical sheet in said light-transmissive type display apparatus may be formed out of light-transmissive beads, and said light-transmissive beads may be distributed unevenly more at the opposite surface side of said coating layer to the light-transmissive base material, and formed into said many fine knoll-shaped projections by being projected from said surface.
The present invention attains the said object by means of a light-transmissive type display apparatus provided with a flat light-transmissive display means and a surface light source device which is disposed at the back of this light-transmissive display means and irradiates said light-transmissive display means from the back with its output light, wherein said surface light source device is composed of a light source for outputting light from its light outputting surface and an optical sheet provided adjacently to said light outputting surface, wherein said optical sheet has one surface of a light-transmissive base material on which a light diffusing sheet is provided and the other surface being covered with a coating layer of light-transmissive materials, and said coating layer contains light-transmissive spherical beads of 1 xcexcm or less in half bandwidth of the distribution of particle diameters, and at least part of these spherical beads are projected from the opposite surface of said coating layer to the light-transmissive base material and are formed into many fine knoll-shaped projections of 1 to 10 xcexcm in height projecting from said surface, and the light outputted from said light outputting surface is inputted from said coating layer side.
Said light diffusing layer of the optical sheet in said light-transmissive type display apparatus may contain light-transmissive spherical beads, and the average particle diameter of the light-transmissive spherical beads in said light diffusing layer may be made larger than the average particle diameter of the spherical beads contained in said coating layer.
The spherical beads contained in said coating layer of the optical sheet in said light-transmissive type display apparatus may be 1 to 10 xcexcm in particle diameter.
The present invention attains the said object by means of a light-transmissive type display apparatus provided with a flat light-transmissive display means and a surface light source device which is disposed at the back of this flat light-transmissive display means and irradiates said light-transmissive display means from the back with its output light, wherein said surface light source device is composed of a light source for outputting light from its light outputting surface and an optical sheet provided adjacently to said light outputting surface, said optical sheet has one surface of a light-transmissive base material on which at least one of a group of plural unit prisms and a group of plural unit lenses is arranged and the other surface being covered with a coating layer formed out of light-transmissive materials, said coating layer is composed of a light-transmissive resin and light-transmissive beads which are dispersed in this light-transmissive resin and are 1 to 10 xcexcm in particle diameter and 1 xcexcm or less in half bandwidth of the distribution of particle diameters, and at least part of said light-transmissive beads are formed into many fine knoll-shaped projections of 1 to 10 xcexcm in height projecting from the opposite surface of said coating layer to the light-transmissive base material by being projected from said surface, and said coating layer is 2 to 20 xcexcm in thickness including said fine knoll-shaped projections, and the ratio of the refractive index of a material forming said light-transmissive beads to the refractive index of the light-transmissive resin in said coating layer is 0.9 to 1.1.
Said light-transmissive beads of the optical sheet in said light-transmissive type display apparatus may be distributed unevenly more at the opposite surface side of said coating layer to the light-transmissive base material and may be projected from said surface.
According to the present invention, since many fine knoll-shaped projections of 1 to 10 xcexcm in height are provided on a coating layer covering the reverse surface opposite to the lens surface of a lens sheet, a gap of 1 to 10 xcexcm is formed between said reverse surface and the flat and smooth surface of a light guide plate, a light diffusing plate, another lens sheet or the like disposed adjacently to said reverse surface, and thereby the distance between said reverse surface and the flat and smooth surface of a light guide plate or the like is kept so that no interference is generated between an advancing light and a reflected light and thus generation of interference fringes or Newton""s rings can be prevented.
The vertical angle of the tops of said prisms or lenses of the optical sheets being in contact with the coating layer of another optical sheet may be as sharp as 100xc2x0 or less.
According to the present invention, since light-transmissive beads are distributed unevenly more at the vicinity of the surface of a coating layer in case of providing many fine knoll-shaped projections of 1 to 10 xcexcm in height by distributing the light-transmissive beads in the coating layer covering the reverse surface opposite to the prism surface of a prism sheet, the invention is economical and efficient thanks to doing with a small amount of beads to be used, and can suppress a phenomenon of deteriorating the primary function of a prism sheet of improving the brightness of a display screen by collecting light in the direction perpendicular to the light outputting surface which phenomenon comes into question in case of forming a light diffusing layer on the reverse surface opposite to its prism surface of a prism sheet. Since the coating layer is hardened and formed in a state where an ink containing light-transmissive beads smaller in specific gravity than the light-transmissive resin is applied to the light-transmissive base material and the light-transmissive beads have come up to the surface of the ink thanks to the difference in specific gravity between them, it is possible to easily and surely distribute the light-transmissive beads unevenly more in the vicinity of the surface of the coating layer.
According to the present invention, since spherical beads are contained in a coating layer which covers the reverse surface opposite to the lens surface or the prism surface of an optical sheet or the reverse surface of an optical sheet having a light diffusing layer on its obverse surface, a small gap is formed between said reverse surface and the flat and smooth surface of a light guide plate, a light diffusing plate, another prism sheet or the like disposed adjacently to said reverse surface, and a light diffusing effect by the spherical beads prevents interference between an advancing light and a reflected light due to a distance between said reverse surface and the flat and smooth surface of a light guide plate or the like and prevents generation of interference fringes or Newton""s rings. And since the spherical beads contained in the coating layer are 1 xcexcm or less in half bandwidth of the distribution of particle diameters, the projections from the reverse surface of an optical sheet vary a little in height and are uniformly in contact with another optical sheet such as a prism sheet or the like, and therefore a trouble is prevented that a prism or the like of another optical sheet is broken by a concentrated load caused by a greatly projected spherical bead.
The vertical angle of the tops of said prisms or lenses of the optical sheets being in contact with the coating layer of another optical sheet may be as sharp as 1000 or less.